Quasi-elliptical band-pass frequency selective surface based on antenna-filter-antenna

Abstract

The invention discloses an antenna-filter-antenna-based quasi-elliptical band-pass frequency selective surface (FSS), which adopts a structure that filtering patch antennas are arranged back to back, so that the FSS can obtain quick descending of a passband edge, an ultra-low profile can be realized, a radiation zero point of the filtering antenna is introduced into the FSS, and the frequency selective surface has the advantages that the filtering patch antennas are arranged back to back; excellent spatial filtering can be realized, and the structure of the AFA successfully avoids the defect that a high-order two-dimensional FSS or a high-order three-dimensional FSS is relatively thick; compared with other FSSs famous in high selectivity, the low-roll-off bandwidth and the high-roll-off bandwidth are only 0.49% fo and 0.0025% fo, which are about 10 times narrower than those of most FSSs.

Description

Technical Field

[0001] The invention belongs to the field of wireless communication and electromagnetic stealth, and mainly relates to a frequency selective surface with good spatial filtering performance, which can be used in the fields of antenna covers, absorbers, electromagnetic shielding and polarization rotation. Background Art

[0002] Frequency selective surface (FSS) is a spatial filter that is periodically arranged in a two-dimensional or three-dimensional structure. It can artificially control the reflection and transmission characteristics of incident electromagnetic waves of different frequencies through design. It is a device with selective filtering characteristics for electromagnetic waves. As a spatial filter, an important performance of FSS is high selectivity. The rapid rolling on both sides of the passband makes the filtering performance better. It has been widely used in antenna design. In the traditional frequency selective surface research method, whether it is a two-dimensional or three-dimensional structure frequency selective surface, in order to obtain higher selectivity, the thickness of FSS must be sacrificed. In response to the contradiction between selectivity and FSS thickness, the researchers proposed a quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna, which can well achieve high selectivity and low profile, so as to have better practical effects in fields such as radar stealth.

[0003] In recent years, the development of FSS in China has been rapid. In order to make the FSS with a periodic arrangement of two-dimensional structures obtain high selectivity, researchers usually realize high-order filters by cascading multi-layer structures. For example: The invention patent with Chinese patent application number 202110109130.9, entitled "Bandpass frequency selective surface structure based on antenna-filter-antenna", discloses a frequency selective surface structure with stable quasi-elliptical filter response and high selectivity. The structure produces a total of four transmission poles and two transmission zeros, with stable quasi-elliptical filter response and high selectivity. The frequency selection unit is composed of a nine-layer cascade structure: a first radiation patch, a first dielectric plate, a first metal floor, a second dielectric plate, a resonant layer, a third dielectric plate, a second metal floor, a fourth dielectric plate, and a second radiation patch. Obviously, the disadvantage of the multi-layer cascade structure is that the thickness of the frequency selection unit is increased, and the overall structural profile is thicker.

[0004] Another method to improve the performance of the frequency selective surface in domestic FSS research is to form the FSS with a 3-D structure. For example: China's invention patent application number 201910331692.0, entitled "A wide passband 3D frequency selective surface", discloses a wide passband 3D frequency selective surface, the purpose of which is to improve the angular stability of this selection surface. The invention is composed of m×n passive resonant units, and each resonant unit structure includes: five layers of dielectric plates and four layers of metal plates. While achieving a steep edge drop passband, the invention improves the angular stability, making it applicable to large incident angles, but the limitations are: the angular stability is general and the overall structural profile is relatively thick. Summary of the invention

[0005] In order to solve the existing problems of this technology, the present invention provides a quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna to solve the technical problem that the high selectivity affects the thickness of the frequency selective surface in the prior art, so that it has the characteristics of high selectivity and ultra-low profile. To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A quasi-elliptical bandpass frequency selective surface based on an antenna-filter-antenna, comprising from top to bottom a first frequency selective surface (1), a first dielectric layer (2), a ground layer (3), a second dielectric layer (4), and a second frequency selective surface (5), wherein the center of each layer of the structure is aligned;

[0007] The first frequency selective surface (1) and the second frequency selective surface (5) are made of the same material, thickness and size, and both include a first metal patch unit (11) and a second metal patch unit (12); the first metal patch unit (11) and the second metal patch unit (12) are connected via a microstrip line;

[0008] The second metal patch unit (12) comprises two open-circuit branch resonators which are arranged up and down and connected to each other; the wavelengths of the two branch resonators are both one-quarter wavelength.

[0009] The first metal patch unit (11) is rectangular.

[0010] The dielectric layer (2) and the dielectric layer (4) are made of exactly the same material, thickness and size.

[0011] The first frequency selective surface (1) is directly printed on the first dielectric layer (2) of the single-layer ground substrate, and the second frequency selective surface (5) is directly printed on the second dielectric layer (4) of the single-layer ground substrate, and both are fed by a 50Ω SMA connector.

[0012] The first dielectric layer (2) and the second dielectric layer (4) are completely identical in thickness, material and size.

[0013] The ground layer (3) is the ground and is directly connected to the first medium layer (2) and the second medium layer (4).

[0014] The middle air layer is 30mm long, 30mm wide and 1oz thick.

[0015] The first dielectric layer (2) and the second dielectric layer (4) are made of F4BTM400 material, with a loss tangent of 0.0023; a length of 30 mm, a width of 30 mm, and a thickness of 1.524 mm.

[0016] The thickness of the first frequency selective surface (1) and the second frequency selective surface (5) are both 1 oz, the material is copper, and the conductivity is 59.6×10MS / m.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The structure of the FSS proposed by the present invention is to place the filter patch antennas back to back. This structure not only enables the FSS to achieve a rapid drop in the passband edge, but also achieves an ultra-low profile. The radiation zero point of the filter antenna is introduced into the FSS, which can achieve excellent spatial filtering. Moreover, the structure of the AFA successfully avoids the disadvantage of high-order two-dimensional FSS or three-dimensional FSS being thicker. Compared with other FSSs known for their high selectivity, the low roll-off bandwidth and high roll-off bandwidth of the present invention are only 0.49% f0 and 0.0025% f0, which are about 10 times narrower than most FSSs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the three-dimensional structure of a quasi-elliptical bandpass frequency selective surface provided in an example of the present invention.

[0020] Figure 2 A schematic diagram of the top layer and side structure of a quasi-elliptical bandpass frequency selective surface provided in an example of the present invention.

[0021] FIG. 3( a ), FIG. 3( b ) and FIG. 3( c ) are three configuration evolutions of the metal patch antenna of the quasi-elliptical bandpass frequency selective surface provided by an example of the present invention.

[0022] Figure 4 The simulation results of three evolution modes of the metal patch antenna with a quasi-elliptical bandpass frequency selective surface provided in the example of the present invention.

[0023] Figure 5 The S-parameter simulation results of the quasi-elliptical bandpass frequency selective surface provided for the example of the present invention.

[0024] Figure 6 The simulation results of the transmission coefficient of the quasi-elliptical bandpass frequency selective surface provided for the example of the present invention varying with the source frequency.

[0025] FIG7(a) is the electric field distribution of the quasi-elliptical bandpass frequency selective surface provided by the example of the present invention at different frequencies; FIG7(b) and FIG7(c) are the current distribution of the quasi-elliptical bandpass frequency selective surface provided by the example of the present invention, respectively. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] The present invention provides a transparent low-loss absorption-through integrated frequency selective surface based on metal fine wires. The metamaterial includes a top frequency selective surface layer 1, a dielectric layer 2, a ground layer 3, a dielectric layer 4 and a bottom frequency selective surface layer 5 from top to bottom. The dielectric layer 2 and the dielectric layer 4 are the same substrates, and are directly connected to the ground layer 3 respectively. The frequency selective surface layer 1 is a filter antenna metal patch directly connected to the dielectric layer 2. The frequency selective surface layer 5 is a filter antenna metal patch that is the same as the frequency selective surface layer 1 and is directly connected to the dielectric layer 4.

[0028] like Figure 1 As shown in FIG. 1 , the antenna is printed on a single-layer ground substrate and fed by a 50Ω SMA connector. The typical microstrip patch antenna selected has the characteristics of low profile, single layer and compactness.

[0029] like Figure 2 As shown, the metal patch on the substrate consists of two parts: one part is a rectangular patch structure (11); the other part is an inverted F-shaped structure (12), which is composed of two open-circuit branch resonators, and the two parts are connected by a bent microstrip line (13). Due to the existence of the combination of these two radiators, the two radiation modes of the antenna can be excited in sequence in the common radiation aperture. Therefore, the entire filtering antenna can be considered to be a mixed-mode antenna.

[0030] To reveal the working principle of the hybrid mode of the studied antenna, Figures 3(a) to (c) show the evolution of the antenna from ANT1 to ANT3.

[0031] The three antennas are specifically defined as:

[0032] (1) ANT1: rectangular patch antenna, as shown in Figure 3(a);

[0033] (2) ANT2: A rectangular patch antenna with an inverted F-shaped open-branch resonator added to ANT1, as shown in Figure 3(b);

[0034] (3) ANT3: Based on ANT2, an inverted F-shaped rectangular patch antenna with an open branch resonator is added. The two inverted F-shaped rectangular patch antennas with open branch resonators are axially symmetrically distributed on a plane, as shown in FIG3(c).

[0035] Reference Figure 2 The dielectric plate and the metal patch size of the present invention are further described in detail:

[0036]

[0037] Wherein, sub_l and sub-w represent the length and width of the first dielectric layer 2 and the second dielectric layer 4 respectively; p and wp1 w represent the length and width of the first metal patch unit 11 respectively; p represents the distance from the top of the first metal patch unit 11 to the bottom of the second metal patch unit 12; the bottom of the first metal patch unit 11 has a rectangular opening, the size of which is l s *w s . p1 represents the distance between the rectangular opening and the left end of the first metal patch 11. w1 and l k1 w2 and l respectively represent the width and length of the open-circuit branch resonator close to the first metal patch; k2 represent the width and length of the open branch resonator farther from the first metal patch; h1 and l0 represent the height and length of the common part between the two open branch resonators; one end of the microstrip line connecting the first metal patch 11 and the second metal patch 12 is led out from the opening of the first metal patch 11, has four sections, and forms three bends. The lengths of the second section, the third section and the fourth section are l respectively. ml1 ,l ml2 ,l ml3 , the size of the first segment is mainly determined by ls, which is l s -w g -w ml ; The other end is connected to the open branch resonator close to the first metal patch; the width of the microstrip line is w ml ;w g Represents the distance between the microstrip line and the lower end of the first metal patch 11. ε r represents the dielectric constant, which is the material parameter of the first dielectric layer 2 and the second dielectric layer 4.

[0038] As shown in Figure 3, it is the specific evolution process of the three antennas. There is no radiation zero point on the achieved gain curve of ANT1, that is, the antenna does not have filtering performance. The filtering performance of the proposed antenna needs to be achieved through two open branches, which provide radiation zero points at the upper and lower band edges of the achieved gain. According to the transmission line theory, a quarter-wavelength open branch resonator will lead to a transmission zero point, thereby introducing a deeply attenuated radiation zero point at the edge of the passband for achieving gain. Therefore, when ANT1 is loaded with a quarter-wavelength branch resonator, that is, ANT2, a radiation zero point will be generated in the upper sideband of the passband. In order to achieve highly selective response on both sides of the passband, a quarter-wavelength branch resonator is loaded on the patch of ANT2, that is, ANT3.

[0039] Antenna structure based on ANT3, such as Figure 1As shown, the AFA structure consists of a receiving antenna ANT3, a bandpass resonant structure and a transmitting antenna ANT3. The common ground with a circular aperture serves as the resonant structure between the two antennas. The through hole in the center of the circular hole connects two patches that provide spatial filtering performance of the component, so that the component has spatial filtering performance. The receiving antenna and the transmitting antenna are selected as filtering elements, and their filtering performance is coupled in the resonant structure, so that a higher-order response can be obtained with fewer layers. The two transmission zero points close to both sides of the passband determine its higher selectivity and more valuable filtering performance. Figure 2 As shown, the entire unit is located at the center of the coordinate system, and the vertical through hole is at a distance of f from the x-axis. x is 8.85mm, from the y-axis f y It is 7mm, and the transmission coefficient and reflection coefficient of FSS under normal incidence can also be known.

[0040] In order to further study the filtering characteristics of FSS, its key geometric parameters are analyzed. The short line close to the patch is called short line I, and the other is called short line II. The length Lk1 of short line I and the length Lk2 of short line II affect the transmission zeros on the upper and lower sides of the passband respectively. The transmission zeros introduced by the two branches can be quantitatively realized by their lengths, making the realization of FSS filtering characteristics more flexible.

[0041] The following simulation experiments are used to further illustrate the technical effects of the present invention:

[0042] 1. Simulation conditions

[0043] Simulation hardware platform: processor Intel(R) Xeon(R) Gold6240 CPU, main frequency 2.60GHz, memory 32GB.

[0044] The software platform is: Windows 10 operating system and HFSS19.0.

[0045] 2. Analysis of simulation content and simulation results

[0046] 2.1. The commercial simulation software HFSS_19.0 was used to simulate the relationship between the reflection coefficient and the realized gain value corresponding to the three gradually evolving antenna models mentioned above and the change of the source frequency. The results are as follows: Figure 4As shown, the left figure shows the relationship between the realized axial gain value and the excitation frequency, with the horizontal axis being the frequency and the vertical axis being the gain; the right figure shows the S11 curve, with the horizontal axis being the frequency and the vertical axis being the S parameter size. It can be seen from the figure that: from the S11 curve of ANT1, it can be seen that it is a traditional patch antenna, but after adding two branches, in addition to the rectangular microstrip patch working in the 4.12GHz mode, the inverted F antenna working in the 4.03GHz mode also plays an important role. The two modes of the developed antenna work together at similar frequencies, effectively maintaining a -10dB impedance bandwidth in the range of 4.02-4.15GHz.

[0047] 2.2. The S parameters of FSS were simulated using the commercial simulation software HFSS_19.0. The results are as follows: Figure 5 As shown in the figure, it can be seen that the proposed FSS can achieve a flat passband and a sharply declining sideband. In the range of 0.006GHz and 0.02GHz, the upper passband and the lower passband can quickly roll off from -3dB to -10dB. At the same time, it can also ensure that the out-of-band suppression is less than -25dB, and has an extremely low profile height of 0.043λ0 while achieving high selectivity.

[0048] 2.3. The commercial simulation software HFSS_19.0 was used to simulate the variation of the FSS transmission coefficient based on AFA with the source frequency. The results are as follows: Figure 6 In order to further study the filtering characteristics of FSS, its key geometric parameters are analyzed. In the definition shown in the figure, the short line close to the patch is called short line I, and the other is called short line II. Figure 6 (a) As can be seen, as the length of Lk1 increases, the upper transmission zero point moves toward low frequency. When the length of short line I Lk1 increases from 11.98mm to 12.38mm, the upper transmission zero point moves toward low frequency. Figure 6 (b) It can be seen that when the length of the open short line Lk2 away from the patch increases, the lower transmission zero moves to the high frequency. This simulation result shows that the transmission zero introduced by the two branches can be quantitatively realized by their lengths, which makes the realization of FSS filtering characteristics more flexible.

[0049] 2.4. The actual electric field and current distribution of FSS were simulated using the commercial simulation software HFSS_19.0, and the results are shown in Figure 7. From the FSS electric field distribution diagram shown in Figure 7(a), it can be seen that the microstrip patch antenna constituting the FSS operates in the TM10 mode at frequencies of 4.04GHz and 4.2GHz. When the FSS operates at 4.064GHz and 4.158GHz, the two branches resonate. From the current distribution diagrams of the FSS at the two radiation zero points proposed in Figures 7(b) and (c), it can be seen that: at the first radiation zero point, the current density on the short line is very high, indicating that most of the energy is concentrated here, while the current on the patch that dominates the radiation is much lower. In addition, it is found that the current distribution on the two radiating sides of the patch is in opposite phase.

[0050] The above simulation results show that the FSS based on AFA in this example has a good filtering response. There are two radiation zeros on both sides of the passband of the actual gain of the filtering antenna used to achieve the filtering function. The radiation zero of the antenna can be obtained through these two transmission zeros, so that the rectangular coefficient is close to 1. The FSS model based on AFA is designed and demonstrated, and the measured results of the FSS are in good agreement with the simulation results, proving that the design method is feasible.

[0051] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna, It is characterized in that From top to bottom, it includes a first frequency selective surface (1), a first dielectric layer (2), a ground layer (3), a second dielectric layer (4), and a second frequency selective surface (5), and the center of each layer of the structure is aligned; The first frequency selective surface (1) and the second frequency selective surface (5) are made of the same material, thickness and size, and both include a first metal patch unit (11) and a second metal patch unit (12); the first metal patch unit (11) and the second metal patch unit (12) are connected via a microstrip line; The second metal patch unit (12) comprises two open-circuit branch resonators which are arranged up and down and connected to each other; the wavelengths of the two branch resonators are both one-quarter wavelength.

2. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The first metal patch unit (11) is rectangular.

3. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The dielectric layer (2) and the dielectric layer (4) are made of exactly the same material, thickness and size.

4. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The first frequency selective surface (1) is directly printed on the first dielectric layer (2) of the single-layer ground substrate, and the second frequency selective surface (5) is directly printed on the second dielectric layer (4) of the single-layer ground substrate, and both are fed by a 50Ω SMA connector.

5. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The first dielectric layer (2) and the second dielectric layer (4) are completely identical in thickness, material and size.

6. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The ground layer (3) is the ground and is directly connected to the first medium layer (2) and the second medium layer (4).

7. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The middle air layer is 30mm long, 30mm wide and 1oz thick.

8. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The first dielectric layer (2) and the second dielectric layer (4) are made of F4BTM400 material, with a loss tangent of 0.0023; a length of 30 mm, a width of 30 mm, and a thickness of 1.524 mm.

9. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that The thickness of the first frequency selective surface (1) and the second frequency selective surface (5) are both 1 oz, the material is copper, and the conductivity is 59.6×10MS / m.

10. The quasi-elliptical bandpass frequency selective surface based on antenna-filter-antenna according to claim 1, It is characterized in that sub_l and sub-w represent the length and width of the first dielectric layer (2) and the second dielectric layer (4), respectively; l p and w p1 represent the length and width of the first metal patch unit (11) respectively; w p represents the distance from the top of the first metal patch unit (11) to the bottom of the second metal patch unit (12); the bottom of the first metal patch unit (11) has a rectangular opening, the size of which is l s *w s ; l p1 represents the distance between the rectangular opening and the left end of the first metal patch unit (11); w 1 and l k1 w represent the width and length of the open-circuit branch resonator close to the first metal patch respectively; 2 and l k2 represent the width and length of the open-circuit branch resonator far from the first metal patch; h 1 and l 0 are the height and length of the common part between two open-circuit branch resonators respectively; One end of a microstrip line connecting the first metal patch unit (11) and the second metal patch unit (12) is led out from the opening of the first metal patch unit (11), has four sections, and forms three bends. The lengths of the second section, the third section, and the fourth section are respectively l ml1 ,l ml2 ,l ml3 , the length of the first segment is determined by ls, which is l s -w g -w ml ; The other end is connected to the open branch resonator close to the first metal patch; the width of the microstrip line is w ml ;w g represents the distance between the microstrip line and the lower end of the first metal patch 11; ε r represents the dielectric constant, which is the material parameter of the first dielectric layer (2) and the second dielectric layer (4); the specific parameter values ​​are as shown in the following table, and the parameter value unit is mm:

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